Stents in general are endovascular prostheses which are used, for example, in the treatment of stenoses. Stents are also known for treating aneurysms.
Stents basically involve a carrier structure which is suitable for supporting the wall of a vessel in an appropriate manner in order to expand the vessel or bridge over an aneurysm. For that purpose stents are introduced into the vessel in a compressed condition and then dilated or expanded at the location to be treated and pressed against the wall of the vessel. Such dilation can be effected, for example, by means of a balloon catheter. Alternatively, self-expanding stents are also known. They are made, for example, from a memory metal such as nitinol which, when a given jump temperature is reached, changes its shape, more specifically in the present case changing from the compressed form to the expanded form.
The desirable properties of a stent are embodied in many ways and in part in very different ways. Expandability of the stent which is as simple as possible is desired, as is ease of positioning thereof. In addition, in the case of balloon-expandable stents, elastic return (recoil) which is as slight as possible after expansion is desired so that the stent does not need to be expanded excessively beyond the desired size. An adequate carrier force is desired in the case of self-expanding stents and also in the case of balloon-expanding stents. In addition, in connection with drug-coated stents, there is a desire for the surface coverage of the vessel wall to be as uniform as possible. Finally, the stent should also involve a certain degree of flexibility about its longitudinal axis in order to suitably move with the vessel. That flexibility, however, should not be at the expense of the carrier force of the stent. The stent should also afford lateral branch accessibility that is as good as possible. In addition, attachment of bars of the carrier structure, so-called fishscaling, is generally undesirable. The list of the desirable properties set forth herein is far from being definitive.
The stent disclosed in U.S. Pat. No. 5,925,061 is also to be found among the many attempts to reconcile the desirable properties of a stent with each other. This US patent shows a whole series of stents of different configurations, inter alia, in FIGS. 6 through 10 a stent with a carrier structure which extends helically around the longitudinal axis of the stent is shown.
In spite of the large number of existing stent structures, there is still a need for the plurality of different desirable properties of a stent to be matched to each other as well as possible for a respective situation of use.
Accordingly, an object of the present invention is to develop a stent of the kind set forth in the opening part of this specification, in such a way that it affords a person skilled in the art a further option in terms of embodying its desirable properties.